How to Measure Weather Temperature

How to Measure Weather Temperature? A Complete Guide

Comparatively, the concept of measuring weather temperature is new, as early scientists didn’t have a quantifying method of measuring and quantifying temperatures. However, in 1714, Daniel Gabriel Fahrenheit invented the thermometer with a standardized scale that effectively quantified temperature, after which Anders Celsius improved it further by incorporating the Celsius scale in 1742. Today, there are different types of thermometers used to measure weather temperature that uses different temperature measuring mechanisms.

According to National Weather Services, weather temperature is one of the most widely measured weather elements in the atmosphere today. People across the globe plan their daily activities and forecast weather patterns based on their locality’s weather temperature. This underlines why having a clear understanding of how to measure weather temperature is essential in running day-to-day activities and averting harsh weather conditions.

Read on to find out everything you need to know about the types of weather thermometers, siting guidelines you should observe, and how to measure weather temperature.

How to Measuring Weather Temperature

It is important to note that weather temperatures get distorted by a host of factors such as wind, sunlight, and other weather elements. That’s the reason why recording 100 percent accurate weather temperature is not entirely possible. However, you should strive to ensure the accuracy of your weather thermometer by following the steps below.

Step 1: Choose your thermometer and the correct site

As discussed earlier, weather thermometers come in different types, shapes, and sizes, each with its own pros and cons. Thus, the first step of measuring weather temperature is choosing a thermometer that you are comfortable with. Keep in mind that the thermometer you choose will determine the accuracy of your temperature readings.

After choosing the thermometer, it is important to choose the correct location to site your thermometer for optimal and accurate readings. The area you choose to site your thermometer should be open, leveled, and representative of the surrounding area. Place your weather thermometer away from obstruction, pavements, and vegetation as they can affect its readings.

Step 2: Place the thermometer in a Stevenson screen

Weather thermometers should not be placed under direct sunlight as they will record higher temperatures than normal thus giving inaccurate data. That’s why National Weather Services recommends that a weather thermometer should be placed under a shade. Placing your weather thermometer in a Stevenson screen is the best way to offer the protection and shading that it needs.

The Stevenson screen was invented by Thomas Stevenson, with the aim of protecting weather thermometers from solar radiation and water damage. The housing is painted white to reflect sunlight, has louvered sides for free airflow, and down swinging doors to protect the thermometer from direct sunlight and wind. Placing your weather thermometer in the Stevenson screen will improve their accuracy.

Step 3: Record maximum and minimum temperatures

Weather temperatures are not static as they keep changing with the change in weather conditions. This explains why you should place both maximum and minimum thermometers on your Stevenson screen. The best maximum thermometer is the mercury-in-glass thermometer while the minimum thermometer is a spirit, ethyl, alcohol, or pentane thermometer with a dark glass.

Both minimum and maximum thermometers should be placed at a 2 degrees angle with their bulbs positioned at the lower end. Once you have placed the two thermometers in your Stevenson screen give them time to rest and record the weather temperature. Consequently, read and record the minimum and maximum temperature readings and calculate the average to find the weather temperature of the day.

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Types of Weather Thermometers

Weather thermometers come in different sizes and shapes, from the ancient liquid-in-glass thermometers to the modern digital thermometers. The different weather thermometers have distinct pros and cons that you should consider when picking the one to purchase.  Outlined below are the common types of weather thermometers.

Mercury-In-Glass Thermometer

Mercury-in-glass thermometers are one of the oldest but widely recognized types of thermometers still used globally. The thermometer was invented in 1714 by Daniel Fahrenheit and consists of a thin glass tube and a glass bulb. Its glass tube is filled with mercury while the empty space is filled with nitrogen or any other gas whose pressure is lower than that of atmospheric pressure.

Mercury-In-Glass Thermometer

The empty space in the glass tube occupied by gases gives leeway for the expansion or contraction of mercury due to temperature changes. Once the weather temperature increases the mercury in the glass tube expands pushing up its level in the tube, while the mercury contracts with a decrease in weather temperature causing its level to lower. The mercury-in-glass thermometer’s tube is calibrated with Celsius, Kelvins, or Fahrenheit temperature scale, which allows you to read the weather temperature.

Mercury in the mercury-in-glass thermometer can be replaced by alcohol or ethyl which is cheaper, less dangerous, and has a low freezing point. However, it is important to note that mercury is more accurate and has a lower boiling point than alcohol or ethyl.

Bimetal Thermometer

Bimetal thermometer, or classic old dial thermometer as it is commonly referred, was developed in 1759 by John Harris. The weather thermometer is widely used across the globe due to its reliability and robustness, making it ideal for use in an automotive and industrial environment. The bimetal thermometer consists of two metal strips connected to each other that respond differently to temperature changes.

Bimetal Thermometer

The bimetal strips are coil-shaped with one of their end fixed in place while the other connected to the measuring device such as a needle. Once the weather temperature around the strips changes, one of the metal strips expands or contracts to cause the needle to move on the calibrated scale to display the weather temperature. The majority of bimetal thermometers are engraved in wooden casings, installed with analog barometers, and hanged on the wall.

Thermoelectric Thermometer

Thermoelectric thermometers measure and display weather temperature using a thermistor, used in various digital devices. The thermistor has an electrical resistance that is dependent on weather temperature. Thus, as weather temperature change the thermistor’s electrical resistance changes resulting in a change in the electrical current strength flowing through the device.

Thermoelectric Thermometer

The electrical current strength is then used to calculate the weather temperature. Thermoelectric thermometers come with either one of the two types of thermistors namely: Positive Temperature Coefficient (PTC) or Negative Temperature Coefficient (NTC). The two thermistors react differently when exposed to weather temperature but both measure temperatures ranging from -90 degrees Celsius to 130 degrees Celsius.

Scales Used to Measure Weather Temperature

Basically, weather temperature is the measure of kinetic energy that the environment or air possess. Temperature is a relative measurement and that’s why reference point based scales are used to accurately measure it. Today, there are mainly three types of scales used to measure weather temperature as outlined below.

  • Fahrenheit Scale

Fahrenheit scale was invented by Daniel Gabriel Fahrenheit, from whom its name is derived, in 1724. The physicist set salty ice water temperature at 0 degrees, ice water temperature at 30 degrees, and human body temperature at 96 degrees. Using his scale, Fahrenheit set boiling water temperature at 212 degrees and later adjusted the freezing water temperature from 30 degrees to 32 degrees.

The adjustments meant that the interval between the boiling and freezing points of water became 180 degrees and the human body temperature 98.7 degrees. The major drawback of the Fahrenheit scale is that it is not the standard SI unit of measurement, and that’s why it is not used in scientific research. Fahrenheit was later replaced by the Celsius scale but it is still used in the United States of America.

  • Celsius Scale

The Celsius scale was invented by Anders Celsius in 1742, in an attempt to improve the Fahrenheit scale. Celsius used water boiling point and ice melting point as his reference temperatures for a consistent and simple thermometer calibration method. Unlike Fahrenheit, the astronomer set the boiling and freezing points at an interval of an even 100 degrees with the water freezing point being 0 degrees and the boiling point being 100 degrees.

Celsius Scale

The Celsius scale is commonly preferred than Fahrenheit scale in scientific research due to its compatibility with the base ten format of the SI unit of metric measurements. Also, the Celsius scale has been incorporated by many countries across the globe other than United States of America.

  • Kelvin Scale

The Kelvin scale was invented by Lord William Kelvin in 1854. The Scottish physicist based the scale on absolute zero degrees where no discernible kinetic energy is detectable and molecular motion halts. The lowest temperature in the Kelvin scale, which is the freezing point, is -237.15 Kelvins, while the boiling point is 373.15 Kelvins.

Similar to the Celsius scale, the Kelvin scale is the standard international system unit of measurements commonly used in scientific research. The Kelvin scale is conveniently used to measure extremely low weather temperatures because it doesn’t have negative numbers.

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Siting Guidelines of Weather Thermometers

The accuracy and reliability of your weather temperature readings solely depend on the location where you site your weather thermometer. Generally, your weather temperature measuring device should be placed in an open space free from any obstruction for optimum performance. Below are the weather thermometer siting guidelines that you must follow for concise and accurate temperature readings.

  • Height

Weather thermometers absorb ambient ground temperatures very easily, which could distort their temperature readings. Also, if placed too high it could pick cool air temperature thus distorting accurate temperature readings. This being the case, the standard height that you should place your weather thermometer is 5 or 6 feet above the ground.

The pole used to support the weather thermometer from the ground should not be a good conductor of heat, as it could affect the thermometer’s readings.

  • Shading

Bimetallic and liquid-in-glass thermometers absorb solar radiation efficiently that the surrounding air, which could affect their readings. That’s the reason why you should avoid placing your weather thermometer under direct sunlight as it will give inaccurate data. Consider placing it under a shade, installing a solar radiation shield, or placing it in a ventilated housing like Stevenson screen.

Besides shielding your thermometer from solar radiation, a shade will protect it against rain or precipitation damage. If using a man-made shade, consider using a white shade with good ventilation to reflect solar radiation and prevent heat accumulation to optimize its performance.

  • Condition of the location

Weather thermometers pick temperatures generated by different cooling and heating sources easily, thus giving faulty temperature readings. This being the case, you should place your weather thermometer in an open and leveled area preferably 10 meters diameter from the nearest obstruction. Also, place the thermometer in an area whose vegetation has been trimmed, as vegetation generates heat which could affect its readings.

Avoid placing your weather thermometer on rocky, steep, and concrete terrain because they affect the performance of the temperature measuring device.

  • Distance from obstruction

A weather thermometer sited near a building will easily pick up the inside temperature of the building, thus affecting accurate temperature readings. A weather thermometer should be placed in a ventilated area with good airflow for optimum performance. National Weather Services recommends that you should place your weather thermometer at a distance four times the height of the nearby building.

Thus, if the nearby building is 6 meters, your thermometer should be 24 meters away from the building. Also, avoid placing your weather thermometer near heat or cool sources for optimum accuracy.  Placing your thermometer in an area with good airflow will enable it to maintain temperature balance with that of the surrounding environment.

Final Thoughts

Measuring weather temperature is essential if you want to plan your daily activities or prepare for harsh weather conditions. The different types of weather thermometers and temperature scales discussed above will allow you to measure temperature in a different way. However, you must ensure that the weather temperatures you record are not only reliable but accurate, by following the later thermometer siting guidelines.




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